With the widespread use of portable color-display devices, there has been a rapidly growing demand for printing in a simple manner photographs or documents that are captured or prepared using such devices in color. This may be realized by a color printing method such as electrophotography, an ink-jet method, or thermal transfer recording. In particular, thermal transfer recording is a suitable method for realizing printing in a simple manner regardless of circumstances, because it enables printing to be performed using a dry process and allows reduced printer size, which increases printer portability. In addition, dyes are used as colorants in thermal transfer recording. This enables the density of images to be controlled by changing the density and gradations of the colorants, which increases the vividness of the images and enables a high color-reproduction capability to be achieved.
Thermal transfer recording is an image-forming method in which a thermal transfer recording sheet constituted by a sheet-like base material and a colorant layer disposed on the base material, the colorant layer including a thermally migratable colorant, is superimposed on an image-receiving sheet including a colorant-receiving layer disposed on the surface thereof, and the colorant included in the thermal transfer recording sheet is transferred to the image-receiving sheet by heating the thermal transfer recording sheet in order to perform recording. In thermal transfer recording, colorants included in the transfer sheet or in an ink composition included in the transfer sheet are critical materials that affect the speed of transfer recording and the quality and preservation stability of the recorded images. There have been reported studies (see PTL 1, PTL 2, and PTL 3) in which high-chroma methine-based magenta coloring matters having high vividness, a high color-reproduction capability and a high color-developing density are used as colorants for the above-described thermal transfer recording (WO92/19684, Japanese Patent Laid-Open No. 05-262062, and Japanese Patent Laid-Open No. 2003-205686). However, it is known that these dyes have considerably poor lightfastness while they have a high chroma and a wide color gamut. Furthermore, when such magenta coloring matters are used in combination with other coloring matters such as a yellow coloring matter and a cyan coloring matter which have been proposed as colorants for thermal transferring, the magenta coloring matters may cause catalytic fading, which increases the rate of deterioration of the other colorants. Accordingly, production of a thermal transfer recording sheet that enables high chroma (i.e., vividness), wide color gamut (i.e., color-reproduction capability or color-developing capability) to be achieved, and good lightfastness to be achieved and the degree of catalytic fading to be reduced has been anticipated.